http://www.nationalparks.org/discover-parks/index.cfm?fa=viewPark&pid=YELL - Yellowstone National Park offers geothermal wonders, such as “Old Faithful," for its visitors. Yellowstone once experienced a massive volcanic eruption that spewed an immense volume of ash. This happened in Yellowstone Park 640,000 years ago and helped shape the park that we know today.